Sherlock tackles a 120-year-old mystery as he wages a deadly battle with Jim Moriarty inside his own mind palace.

This mind-bending, time-travelling one-off special could have fallen horribly flat. However, both the case-within-the-case and the broader Inception-style investigation by Sherlock into Moriarty’s apparent return from the dead, delivered on Steven Moffat and Mark Gatiss’s gleeful description of this story being like having their cake and eating it.

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The Victorian part of the story consists of two linked mysteries. The Abominable Bride serves as a proxy for Sherlock’s assessment of how Moriarty could possibly have survived blowing his own brains out. The murder of Lord Eustace Carmichael ties in Mary Watson and Mycroft as the Bride is literally unveiled as an instrument of the Suffragette movement.

As Sherlock digs deeper, peeling back layer after layer of his dreams, Moriarty infiltrates himself into his mind palace, leading to a confrontation at the Reichenbach Falls. Watson helps his friend overcome his mortal foe once more.

Waking up in the real world at last, Sherlock determines that Moriarty really is dead but says he now knows his next move. The game is on – again.

(Picture: BBC)

Looks familiar?

It wasn’t just Sherlock who was experiencing a sense of deja vu during his mind palace adventures. Moffat and Gatiss also crowbarred numerous references to both the original stories and the current series into this episode for the fans to pore over.

The episode’s titular adventure, The Abominable Bride, is an untold story mentioned by Holmes in The Musgrave Ritual. There are direct references to The Blue Carbuncle and The Five Orange Pips. And, of course, we are treated to the ‘real’ confrontation between Holmes and Moriarty at the Reichenbach Falls, as related in The Final Problem, as well as a faithful reproduction of Watson and Mike Stamford’s meeting at the Criterion (from A Study in Scarlet) which leads to John’s introduction to Sherlock.

Fans of the original literary works will also be familiar with a number of other references, including Watson’s description of London as ‘that great cesspool’ and the use of the classic phrases ‘the game is afoot’ (the modern series uses ‘the game is on’) and ‘elementary, my dear Watson’.

And, in addition to the inclusion of Mycroft, Mary, Mrs Hudson, Molly Hooper, Anderson, Stamford and Irene Adler, we also had cameo returns for two characters from John and Mary’s wedding in The Sign of Three: Janine the bridesmaid (and Charles Augustus Magnussen’s PA) and Billy the page boy.

(Picture: BBC)

Did we miss him?

After a two-year absence, this was a clever way to bring Sherlock back to our screens with a period adventure disguising a story that dealt with the series three finale’s cliffhanger of Moriarty’s return while also recalling previous adventures and characters.

The two Victorian cases themselves were almost secondary to the overall story but gave the production team the opportunity to provide us with all the trappings of the original Conan Doyle stories, from its period setting and wardrobe (and Victorian Lestrade’s meaty mutton chops!) to fog-bound London streets, telegrams, hansom cabs, steam trains and a foreboding Gothic church. Coupled with Moffat and Gatiss’s quick-fire, knowing and frequently tongue-in-cheek dialogue, this was a sumptuous treat to usher in 2016.

In both the Victorian and contemporary settings, it’s a delight to watch the easy chemistry between Benedict Cumberbatch and Martin Freeman, while Andrew Scott’s deranged Moriarty lights up his scenes with Sherlock. Watson is acknowledged here as more of a partner than a stooge, and the recognition of Mary’s capabilities also suggests a significant role for her going forward.

With filming on series four due to start in the spring, we may not have to wait another two years for more new Sherlock. January 2017, perhaps?

To paraphrase Moriarty’s mocking question, have we missed Sherlock? Yes, we have. And it’s great to have him back again.